Anywho, the Pern dragons are hard to place since there's been a lot of retconing going on. Originally Ramoth was 45 meters in length. There's an illustration in one of the guide books showing Ramoth to be only slightly smaller than an L-1011 jumbo jet.

Yet in later works, Ramoth was only 65 feet in length. A radical size reduction.

Smaug is a wyvern, not a dragon. Although this changed between the brief scene in An Unexpected Journey and The Desolation of Smaug./If you're going to compare similar creatures at least get them right.